1. Field of the Invention
The present invention relates to a boring bit, and particularly to a boring bit which is adapted to be mounted on a rotary tool and which is suitable to bore a semi-rigid and relatively fragile material such as a foam plastic.
2. Description of the Prior Art
Conventionally, when a communication cable, etc. is underlaid, a sealer such as expandable resin is used for supporting the communication cable within a cable duct and for preventing rats or water from entering the cable duct. For this reason, in order to extend the communication cable or to change the same to a new one, it is necessary to remove a semi-rigid and relatively fragile wall made of expandable resin. Normally, as shown in FIG. 9, to remove a wall W made of an expandable resin-based sealer, a chisel-like tool 41 is driven into the wall W in a direction parallel to a longitudinal direction of a cable C so as to bore and break the wall W. In FIG. 9, numeral 42 designates a hammer, numeral 41a designates a through-hole through which a driver (not shown) is inserted to rotate or prize the tool 41, and alphabet U designates a pad made of urethane, etc. and stuffed for defining a space into which the expandable resin-based sealer is injected. In FIG. 9, a pad on the side of an end opening has been previously removed by a telephone and radio plier or the like. Alternatively, a drill or a fret saw has been used for boring and breaking the wall W.
However, with the conventional measure, the operation for boring and removing the wall must be performed manually by a number of operation steps. In addition, a surface coating covering the cable may be accidentally damaged during the boring operation, resulting in that the cable is cut. The possibility of damage on the cable is particularly increased when the drill or the fret saw is used.